The present invention relates generally to control devices for determining the relative position of two objects, and particularly to a correction selection device which allows operating personnel to simply select the correction value to be used by the control device.
In numerically controlled machines, such as machine tools, for example machine operation is controlled by a programmed controller. The programmed controller directs a forming tool to predetermined positions, as established by the desired dimensions of the finally tooled workpiece. In addition to the desired dimensions of the finished workpiece, variations in tool geometry must be taken into consideration in determining the path of the forming tool commanded by the controller. Such tool geometry corrections are known as tool radius corrections or, in brief, tool corrections. "Numerical Control in Manufacturing", 1963 by Frank W. Wilson, McGraw-Hill Book Company, New York, Library of Congress Catalog Card Number: 63-15105; and "Numerically Controlled Machine Tools ", 1965 by Morse and Cox, Published by American Data Processing, Inc., Detroit, Library of Congress Catalog Card Number: 65-21222 provide further information as to the state of the art.
Because numerically controlled machines preferably form the workpiece, insofar as possible, automatically and without manual intervention, a programmed controller is used to determine coordinates of the tooled workpiece. Corrections which are due to differing tool dimensions are often entered manually. Thus, for example, the radius of a milling tool is often added to or subtracted from the desired workpiece dimension as necessary. The sign (plus or minus) of the specific coordinates and the direction of movement of the tool or of the workpiece are critically important in determining the proper tool correction, and such corrections should be made in accordance with standard specifications (see, e.g., West German Normblatter DIN No. 66 025, Beuth-Vertrieb GmbH, Berlin, West Germany). Similarly, in computing the tool correction it must be taken into account whether the tool moves on an outside edge of the workpiece or in a tool recess along the tooling path. Because tool correction is a function of such constantly changing variables as workpiece geometry and feed direction, the operator must use great care in determining tool corrections. Erroneous tool corrections are frequently the cause of serious mistakes which can irretrievably damage workpieces.